1. Field of the Invention
This invention relates to a method of making a semi-conductor device whether in elements or integrated circuit form and wherein, the semi-conductor element or elements are completely protected from the external atomsphere.
2. Description of the Prior Art
In order to protect a semi-conductor element from the external atmosphere, it has been proposed that the semi-conductor element be directly buried or embedded within a molding material during fabrication of the semi-conductor device. In this case, however, since thermal expansion coefficients of the molding material and the semi-conductor element are different, a stress may be applied to the semi-conductor element and the resultant strength given thereto due to the change of temperature when the semi-conductor element is molded or during operation of the semi-conductor device after molding. As a result, the semi-conductor element may often be damaged or the lead wires of the semi-conductor device internally of the molded body may be disconnected from the external lead extending inwardly thereof, or the internal lead may be broken.
To eliminate these disadvantages, a plastic sealed split casing, cavity type molded semi-conductor device has recently been developed which avoids the direct molding of the semi-conductor element by embedding the semi-conductor element with the package header.
Two examples of conventional cavity molded type semi-conductor devices are shown in FIGS. 1 and 2. The description of the first semi-conductor device of FIG. 1 is described in conjunction with its method of fabrication. A semi-conductor element 2 is mounted on a header 1 previously formed or molded of plastic insulating material, the semi-conductor element 2 being positioned within the central cavity 8 within the header 1. An external lead frame formed of copper, Kovar or the like comprising external leads 3 and 3' is mounted on the header 1 by means of a plastic system binder 4. Thereafter, the internal lead wires 5 and 5' which may be formed of aluminum, gold or the like are bonded to the semi-conductor element 2 and to the inner ends of the external leads 3 and 3' respectively. Finally, a plastic cap 7 having a hollow or recessed portion 6 defining an upper cavity is mounted on the header 1 through a plastic system binder 8 to seal the semi-conductor element 2 from the atmosphere and pressure application to the plastic system binders 4 and 8. The confronting surface port of the header 1 and the cap 7 are thus plastically sealed as are the external leads 3 and 3' which extend through the sealed area from the internal cavity to the ambient atmosphere.
With respect to the second type of cavity molded semi-conductor device as shown in FIG. 2, with respect to its method of manufacture, a semi-conductor element 2 is mounted on a header 11 with a caviity 19, the header in this case being molded with the external leads 3 and 3' of the lead frame being embedded within the header 11 during molding, the header 11 being molded by conventional molding processes using a molder material of powdered epoxy resin. Thereafter, the internal lead wires 5 and 5' are bonded to the semi-conductor element 2 and the external leads 3 and 3' of the lead frame, respectively. Finally, an insulative cap 17 is mounted to the header 11 overlying cavity 10 by way of an epoxy resin binder 14 under the application of heat and pressure.
However, since the cavity molded type semi-conductor devices thus obtained have poor adherence between the external lead frame, the binder and the molding material forming the header and the cap relative to one another, it is difficult to assure that the semi-conductor element or elements within the internal cavity are protected from the external atmosphere. For this reason, such fabricating processes are not generally employed.